The present disclosure relates to toners suitable for electrophotographic apparatuses and processes for making such toners.
Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. These toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Polyester EA low melting toners, including ultra low melting (ULM) toners having desired low temperature fusing performance, have been prepared utilizing amorphous and crystalline polyester resins wherein the addition of the crystalline polyester resin to the amorphous polyester resin imparts a lower melting temperature to the polyester toner. An example of such a low melting polyester toner is described in, for example, U.S. Pat. No. 6,830,860, the disclosure of which is hereby incorporated by reference in its entirety. However, the addition of the crystalline polyester resin to the amorphous polyester resin may cause a lowering of the charging performance of the toner, particularly in higher temperature and/or higher humidity conditions. This may be due, in part, to the crystalline component migrating to the surface of the toner particle during coalescence at a temperature around the melting point of the crystalline resin and interfering with toner charging in high temperature and/or high humidity conditions.
It is known that charge control agents (CCAs) such as organic and/or organometallic complexes may improve the charging performance of conventional melt mixed toners wherein (i) the CCA is added internally to the toner formulation during the melt mixing process, or (ii) blended externally to the toner surface together with other external additives, for example silica and/or titania particles. For EA toners, the challenge of incorporating similar CCAs into said EA toner formulations is heightened by the difficulty in reducing the CCAs to submicron size and incorporating said CCAs in an aqueous medium.
Means for improving toner charge independent of the selection of resin properties and process conditions remain desirable.